Method and composition for plasma etching of a self-aligned contact opening

ABSTRACT

A method of forming a self-aligned contact opening in an insulative layer formed over a substrate in a semiconductor device involves etching the insulative layer with at least one fluorocarbon and ammonia.

FIELD OF THE INVENTION

[0001] The present invention relates to a process for etching aself-aligned contact opening in a semiconductor device, and moreparticularly, to a method of plasma etching to prevent build up ofundesirable polymers during contact formation. The invention alsorelates to a composition useful in the method of plasma etchingdescribed herein, as well as to the semiconductor structures formedthereby.

BACKGROUND OF THE INVENTION

[0002] In the formation of contact openings or vias in semniconductordevices used to provide metal-to-metal or conductive layer-to-conductivelayer contacts, it is often necessary to etch through one or more layersof insulative material formed over a substrate. FIG. I shows a crosssection of a portion of a semiconductor device 10 in an intermediatestage of fabrication. The integrated circuit wafer section 10 has asubstrate 12. The substrate is formed of a semiconductor material, forexample silicon, or a semniconductor material over an insulator, forexample silicon-on-insulator (SOI). Field oxide regions 13, transistorgate stacks 15, side wall spacers 17 protecting the gate stacks, anddoped regions 19 are formed over the substrate. A layer of insulatingmaterial 21, which is usually a type of glass oxide available in theart, for example, Boro-Phospho-Silicate Glass (BPSG), or silicon oxidematerial such as silicon dioxide or Tetraethylorthosilicate (TEOS) isformed over the substrate 12. The layer of insulating material 21 may,in actuality, be formed as one or more layers of insulating material of,for example, BPSG, TEOS or silicon dioxide. The insulating layer 21 maybe anywhere from a few hundred Angstroms to several thousand Angstromsin thickness. Formed over the insulative layer is a photoresist maskinglayer 23 using available photoresist materials. The photoresist layer 23has a patterned opening 25 corresponding to the outline represented bythe dotted lines shown in FIG. 1. The patterned opening forms theoutline of a self-aligned contact (SAC) opening which is thereaftercreated. The SAC opening will provide access to the substrate 12 throughthe insulative layer 21.

[0003] Referring to FIG. 2, a plasma etch is then conducted to form theSAC opening 27, using the patterned opening 25 of the photoresistmasking layer 23 as a guide. The patterned opening 25 generally followsthe outline of the sides of the spacers 17 to align the etch for thecontact opening. During the etching process, one or one fluorocarbonsare introduced into a chamber containing the semiconductor device 10.Under suitable conditions ionic and neutral etchants are then formed toetch the insulative layer 21 so as to form the opening 27.Unfortunately, under prevailing conditions the reaction of theseetchants and other species with the insulative material of layer 21produces a polymer layer 29 on the bottom and side wall spacers ofopening 27 as a reaction product. A thin accumulation of polymer layer29 along the sides of the side wall spacers 17 may be desirable toprevent subsequent erosion of the spacers. However, a build up ofpolymer layer 29 at the bottom of the SAC opening 27 can cause anundesirable phenomenon known as “etch stop”, in which further etchingthrough the insulative layer 21 to the surface of the substrate 12 isprevented by this polymer layer build up 29. In effect, the etch stoppolymer layer 29 formed from the insulative layer can significantlyinhibit suitable formation of the contact opening 27.

[0004] Attempts have been made to prevent etch stop during contactopening formation. For example, it is known to add oxygen (O₂) to themixture of fluorocarbon gases which are introduced into the reactionchamber. As a result, the etch rate of insulative material, e.g. oxide,has been shown to increase. The addition of oxygen appears to beaccompanied by an increase in the density of the fluorine atoms in theetchant discharge. However, the use of too much oxygen may undesirablydilute the fluorine concentration, and thereby decrease the etch rate.Oxygen may also be utilized to clean polymer debris from the bottom ofthe contact opening after exposure to the fluorine-based etchant plasma.Nitrogen (N₂) has also been utilized for cleaning residual debris afterthe etching process.

[0005] What is now needed in the art is a new method of forming aself-aligned contact opening in a semiconductor structure which cansubstantially eliminate etch stop problems. Also needed is a newcomposition which can be utilized in conjunction therewith.

SUMMARY OF THE INVENTION

[0006] In accordance with one aspect of the invention a method isprovided for forming an opening in an insulative layer formed over asubstrate in a semiconductor device in which the insulative layer isetched with ammonia and at least one fluorocarbon. The processparameters hereinafter described will substantially reduce or eliminatethe formation of an “etch stop”.

[0007] Also in another aspect the invention provides a compositionsuitable for use in etching an insulative layer formed over a substratein a semiconductor device. The composition comprises a gaseous mixtureof at least one fluorocarbon and ammonia.

[0008] In another aspect the invention provides a process of forming anopening in an insulative layer formed over a substrate in asemiconductor device. A patterned photoresist mask layer is first formedover the insulative layer. A self- aligned contact opening is thenetched in the insulative layer through an opening in the patternedresist layer. The opening is etched through to the substrate using acombination of ammonia and at least one fluorocarbon.

[0009] In another aspect the invention provides a method of preventingetch stop during etching of a semiconductor device which comprisesadding ammonia to at least one fluorocarbon which is utilized for theetching.

[0010] In another aspect the invention provides a method of preserving aside wall spacer surrounding a gate stack during a self-aligned contactetch. The side wall spacer is contacted with a combination of at leastone fluorocarbon and ammonia so as to form a protective layer thereover.The protective layer prevents erosion of the spacer as the contactopening is formed through to the substrate upon which the gate stack hasbeen formed.

[0011] In another aspect the invention provides a method of forming aconductive plug inside a contact opening in an insulative layer betweenadjacent gate stacks formed over a substrate in a semiconductor device.The insulative layer is contacted with a plasma etchant mixturecontaining ammonia and at least one fluorocarbon at a pedestaltemperature within the range of about −50 to about 80 degrees Celsius soas to form a self-aligned contact opening in the insulative layerbetween the gate stacks without an etch stop. The contacting furtherforms a protective or passivating (nitrogen containing) layer overopposed side wall spacers which have been formed at the gate stacks. Aconductive plug is then deposited inside the opening such that the plugis separated from the side wall spacers by the protective layer.

[0012] These and other advantages and features of the present inventionwilt become more readily apparent from the following detaileddescription and drawings which illustrate various exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a cross sectional view of a semiconductor device in anintermediate stage of fabrication.

[0014]FIG. 2 is a cross sectional view of the device shown in FIG. 1 ina further stage of fabrication.

[0015]FIG. 3 is a cross sectional view of a semiconductor device whichutilizes the method and composition of the invention.

[0016]FIG. 4 is a cross sectional view of a semiconductor deviceaccording to a further embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Reference herein shall be made to the term “substrate,” which isto be understood as including silicon, a silicon-on-insulator (SOI) orsilicon-on-sapphire (SOS) structures, doped and undoped semiconductors,epitaxial layers of silicon supported by a base semiconductorfoundation, and other semiconductor structures. In addition, whenreference is made to a “substrate” in the following description,previous process steps may have been utilized to form arrays, regions orjunctions in or over the base semiconductor structure or foundation. Inaddition, the semiconductor need not be silicon-based, but could bebased on silicon-germanium, germanium, indium phosphide, or galliumarsenide. The term “substrate” as used herein may also refer to any typeof generic base or foundation structure.

[0018] Referring again to the drawings, FIG. 3 illustrates the method ofthe invention which mitigates etch stop problems. According to oneembodiment, there is provided a method of forming a contact openingusing at least one fluorocarbon. It is desirable that the contactopening be a self-aligned contact (SAC) opening, that is, an openingwhich is self-aligned between two successive gate stack structures.Preferably, at least two or more fluorocarbons are utilized, and in someembodiments at least three or more may be used as part of the invention.The fluorocarbon(s) may be chosen from those available in the art forplasma etching. Suitable fluorocarbons therefore include at least onemember selected from the group consisting of fluorinated carbons,fluorohydrocarbons, chlorofluorocarbons and chlorofluorohydrocarbons.Non-limiting examples include such compounds as C₄F₈, C₄F₆, C₅F₈, CF₄,C₂F₆, C₃F₈, CHF₃, and CH₂F₂, and the like. Preferably, one or more ofthe compounds CF₄, CHF₃, and CH₂F₂ are utilized.

[0019] The fluorocarbon(s) are introduced with ammonia (NH₃) in areaction chamber 30 together with the portion of the semiconductordevice shown in FIG. 3. The chamber may be any suitable reaction vesselavailable for plasma etching. The ammonia may be obtained from anysuitable source. It has now been shown that the combination of at leastone fluorocarbon, together with ammonia, is not only effective informing the contact opening 27 shown in FIG. 3, but is also effective inmitigating against etch stop, i.e. the problem illustrated in FIG. 2.

[0020] The fluorocarbon(s) and ammonia are introduced into a suitablereaction chamber along with the semiconductor device. The reactionchamber pedestal may be set at an operating temperature within the rangeof about −50 to about 80 degrees Celsius, with about 0 to about 80degrees Celsius being preferred. Operating pressure is typically withinthe range of about 30 to about 60 milliTorrs, with about 40 to about 50milliTorrs being more preferred, and about 45 milliTorrs beingparticularly desirable. About 600 watts of power is typically applied tothe reaction chamber, but the wattage can vary within a range of about500 to about 1500 watts.

[0021] The fluorocarbon(s) and ammonia are introduced into the reactionchamber at a flow rate which will both allow formation of theself-aligned contact (SAC) opening 27 and prevent or reduce etch stopproblems. In some embodiments, elimination or reduction of the etch stopproblem may be quantifiable by the reduction in time it takes tocomplete formation of the opening, for example. The flow rates may varyslightly, but a ratio of the flow rate for each fluorocarbon to the flowrate of ammonia should typically be within the range of about 2:1 toabout 40:1 (with flow rate being measured as scc/minute or sccm). It ispreferred that the flow rate ratio not be less than about 3:1. Morepreferably, the flow rate ratio should be within the range of about 3:1to about 20:1, and even more preferably about 4:1 to about 10:1.

[0022] Actual flow rates for each of the individual fluorocarbon(s)utilized to form the SAC opening 27 will usually be within the range ofabout 10 to about 50 sccm, with about 10 to about 40 sccm beingpreferred. The flow rate will vary according to the particularfluorocarbon being utilized, and different fluorocarbons may havedifferent flow rates. For example, when CF₄ is utilized, a flow rate ofabout 15 to about 20 sccm is preferred, with about 16 to about 18 sccmbeing more preferred. When CHF₃ is utilized, a flow rate of about 35 toabout 45 sccm may be preferred, with about 37 to 42 sccm being even morepreferred. When CH₂F₂ forms part of the etchant plasma, a flow rate ofabout 10 to about 15 sccm is preferred, with about 11 to about 14 sccmbeing more preferred. In some embodiments of the invention, it may bedesirable to utilize at least two of the foregoing fluorocarbons, andpreferably all three at the flow rates already set forth.

[0023] The flow rate for the ammonia will usually be at least about 2sccm, and should normally not exceed about 6 sccm. An upper limit flowrate of about 5 sccm is generally preferred. A flow rate range for theammonia of about 2 sccm to about 4 sccm is especially desirable. Theflow rates of both ammonia and the fluorocarbon(s) may be adjusted so asto yield the flow rate ratios previously described. An ammonia flow rateabove about 8 sccm is generally not preferred because at this rate theresultant reactant mixture can sometimes cause loss of selectivity tothe gate stack and/or spacer, and may also result in the etched openingnot being self-aligned to the gate stacks and/or the side wall spacers.

[0024] One or more of the fluorocarbons and the ammonia may beintroduced into the reaction chamber substantially simultaneously, orsuccessively. The order of introduction should be consistent with theinvention's goals of eliminating etch stop, while providing a SACopening 27 to the substrate 12 in the device 10.

[0025] Other etchant gases which may be introduced into the reactionchamber together with the foregoing ammonia and fluorocarbon(s) caninclude oxygen, nitrogen and other compounds which are generallyavailable in plasma etching.

[0026] After the etching process is complete such that the self-alignedcontact opening 27 is formed, then the photoresist mask layer may beremoved using available methods.

[0027] As a result of the invention, the device shown in FIG. 3 has aself-aligned contact opening 27 that is formed without etch stopproblems. Moreover, the reactant mixture of fluorocarbon(s) and ammoniaproduces a thin protective layer 35 along the sides of the contactopening 27 defined by the sides of the insulative layer and the sidewall spacers 17. The protective layer 35 is a polymeric material formedas a result of the reaction between the reactant mixture and theinsulative layer and the side wall spacers, respectively. Formation ofthis protective layer 35 helps to prevent erosion and destruction of theside wall spacers during the etching process and thereafter, and istherefore desirable. The protective layer 35 is typically on the orderof just a few Angstroms in thickness, e.g. about 5-50 Angstroms.

[0028] In contrast to the side wall spacers, substantially no layer isformed at the bottom of the opening 27. Without being bound by anyparticular theory, it appears that any de minimis layer of residue thatmay be formed is rather quickly eliminated as a result of continuouscontact with the reactant mixture of the invention. Perhaps this is dueat least in part to the differing chemical components which make up theinsulative layer, in contrast to the side wall spacers upon theprotective layer 35 is formed.

[0029] A further embodiment of the invention is shown now with referenceto FIG. 4. A conductive plug 37 may be formed in the contact opening 27after completion of the etching process. The conductive plug may beformed using a conductive metal such as tungsten, for example, usingtungsten hexafluoride (WF₆) and silane (SiH₄) using available depositiontechniques. Formation of the conductive plug may be proceeded bytitanium deposition and annealing to coat the inside of the contactopening 27 in which the plug is formed. Titanium deposition will form athin contact layer 39, e.g. about 5-50 Angstroms, over the active region19 of the substrate 12. This contact layer will in turn act as aprotective barrier to prevent free fluorine and tungsten atoms frompenetrating into the substrate 12 at the active region site 19 duringformation of the conductive plug 37.

[0030] After deposition of the conductive plug 37, the top of the plugmay be co-planarized with the top of the insulative layer 21 usingchemical mechanical planarization (CMP) techniques, if desired. Anoptional conductive metal runner can also be provided over the plug 37using available materials, e.g. aluminum, and methods (not shown in FIG.4). As a result of the method and composition of the invention using thereactant mixture to etch the contact opening 27, the conductive plug 37adheres more effectively inside the contact opening 27. In particular,the protective layer 35 prevents erosion of the side wall spacers 17which could materially detract from the performance of the plug 37 andthe gate stacks 15.

[0031] The following examples illustrate certain preferred embodimentsof the invention, but should not be construed as limiting the scopethereof.

EXAMPLE 1

[0032] In this example, a self-aligned contact opening was formed in thedevice illustrated in FIG. 3. Plasma etching was conducted in a reactionchamber set at 600 watts, 45 milliTorr operating pressure, and 40 Gauss.Operating temperature was in the range of 0 to 50 degrees C. Thefollowing fluorocarbons were introduced into the reaction chambertogether with ammonia, at the following flow rates: CF₄ 18 sccm CHF₃ 40sccm CH₂F₂ 13 scccm NH₃ 4 sccm

[0033] Under the foregoing conditions, a self-aligned contact openingwas formed in the device shown in FIG. 3 without etch stop.

EXAMPLE 2

[0034] In this example, the same operating parameters and reactionconditions were utilized as set forth in Example 1, except that the flowrate of ammonia (NH₃) was 2 sccm. Under these conditions, a suitableself-aligned contact opening was also formed without etch stop.

EXAMPLE 3 (Comparative Example)

[0035] In this example, the same operating parameters and reactionconditions were utilized as set forth in Example 1, except that the flowrate of ammonia (NH₃) was 8 sccm. Under these conditions, loss of etchselectivity to gate stack and sidewall spacer was observed.

EXAMPLE 4 (Comparative Example)

[0036] In this example, the same operating parameters and reactionconditions were utilized as set forth in Example 1, except that the flowrate of ammonia (NH₃) was 0 sccm. Under these conditions, etch stop wasobserved.

[0037] The foregoing description is illustrative of exemplaryembodiments which achieve the objects, features and advantages of thepresent invention. It should be apparent that many changes,modifications, substitutions may be made to the described embodimentswithout departing from the spirit or scope of the invention. Theinvention is not to be considered as limited by the foregoingdescription or embodiments, but is only limited by the construed scopeof the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A method of forming an opening in an insulativelayer formed over a substrate in a semiconductor device, comprisingetching said insulative layer with ammonia and at least one fluorocarbonso as to form said opening.
 2. The method of claim 1, wherein saidmethod is performed to produce a self-aligned contact opening.
 3. Themethod of claim 1, wherein said etching includes plasma etching.
 4. Themethod of claim 3, wherein said etching is performed within atemperature range of about −50 to about 80 degrees Celsius.
 5. Themethod of claim 4, wherein said etching is performed within atemperature range of about 0 to about 50 degrees Celsius.
 6. The methodof claim 4, wherein said contacting is performed at an operatingpressure of about 25 to about 60 milliTorrs.
 7. The method of claim 4,wherein said contacting is performed at an operating pressure of about40 to about 50 milliTorrs.
 8. The method of claim 1, wherein saidcontacting is performed through a patterned photoresist mask.
 9. Themethod of claim 1, wherein said fluorocarbon is at least one memberselected from the group consisting of fluorinated carbons,fluorohydrocarbons, chlorofluorocarbons and chlorofluorohydrocarbons.10. The method of claim 9, wherein said fluorocarbon is at least onemember selected from the group consisting of C₄F₈, C₄F₆, C₅F₈, CF₄,C₂F₆, C₃F₂, CHF₃, and CH₂F₂.
 11. The method of claim 10, wherein saidfluorocarbon is at least one member selected from the group consistingof CF₄, CHF₃, and CH₂F₂.
 12. The method of claim 1, wherein said methodis performed without forming an etch stop.
 13. The method of claim 12,wherein said method does not remove side wall spacers which are formedalong the sides of a gate stack and which align said contact opening tosaid substrate.
 14. The method of claim 1, wherein said method does notremove side wail spacers which are formed along the sides of a gatestack and which align said contact opening to said substrate.
 15. Themethod of claim 9, wherein said fluorcarbon(s) and said ammonia areflowed into a reaction chamber containing said semiconductor device suchthat the flow rate ratio of said at least one fluorocarbon to saidammonia is not less than about 3:1.
 16. The method of claim 15, whereinthe flow rate ratio of said at least one fluorocarbon to said ammonia iswithin the range of about 3:1 to about 20:1.
 17. The method of claim 16,wherein said flow rate ratio is within the range of about 4:1 to about10:1.
 18. The method of claim 11, wherein said fluorocarbon is at leasttwo members selected from the group of CF₄, CHF₃, and CH₂F₂.
 19. Themethod of claim 18, wherein said fluorocarbons comprise CF₄, CHF₃, andCH₂F₂.
 20. The method of claim 11, wherein said fluorocarbon is CF₄which is flowed into a reaction chamber at a flow rate of about 15 toabout 20 sccm.
 21. The method of claim 18, wherein said fluorocarbon isflowed into a reaction chamber at a flow rate of about 18 sccm.
 22. Themethod of claim 11, wherein said fluorocarbon is CHF₃ which is flowedinto a reaction chamber at a flow rate of about 35 to about 45 sccm. 23.The method of claim 22, wherein said fluorocarbon is flowed into areaction chamber at a flow rate of about 40 sccm.
 24. The method ofclaim I 11, wherein said fluorocarbon is CH₂F₂ which is flowed into areaction chamber at a flow rate of about 10 to about 15
 25. The methodof claim 24, wherein said fluorocarbon is introduced at a flow rate ofabout 13 sccm.
 26. A composition suitable for use in etching aninsulative layer formed over a substrate in a semiconductor device, saidcomposition comprising a gaseous mixture of at least one fluorocarbonand ammonia.
 27. The composition of claim 26, wherein said fluorocarbonis at least one member selected from the group consisting of carbontetrafluoride, fluorohydrocarbons, chlorofluorocarbons andchlorofluorohydrocarbons.
 28. The composition of claim 27, wherein saidfluorocarbon is at least one member selected from the group consistingof C₄F₈, C₄F₆, C₅F₈, CF₄, C₂F₆, C₃F₈, CHF₃, and CH₂F₂.
 29. Thecomposition of claim 26, wherein said fluorocarbon is at least onemember selected from the group consisting of CF₄, CHF₃, and CH₂F₂. 30.The composition of claim 29, wherein said fluorocarbon is at least twomembers selected from the group consisting of CF₄, CHF₃, and CH₂F₂. 31.The composition of claim 30, wherein said fluorocarbon is a combinationof CF₄, CHF₃, and CH₂F₂.
 32. The composition of claim 24, wherein saidcomposition does not remove side wall spacers of a gate stack which isalso formed over said substrate.
 33. The composition of claim 26,wherein said composition is flowed into a reaction chamber containingsaid semiconductor device such that the flow rate ratio of saidfluorocarbon to said ammonia is not less than about 3:1.
 34. Thecomposition of claim 33, wherein said flow rate ratio is within therange of about 3:1 to about 20:1.
 35. The composition of claim 36,wherein said flow rate ratio is within the range of about 4:1 to about10:1.
 36. A process for forming an opening in an insulative layer formedover a substrate in a semiconductor device, comprising: forming apatterned photoresist mask layer over said insulative layer; etching anopening in said insulative layer through an aperture in said patternedresist layer, wherein said opening is etched through to said substrateusing a combination of ammonia and at least one fluorocarbon.
 37. Themethod of claim 36, wherein said etching is performed to produce aself-aligned contact opening in said insulative layer.
 38. The processof claim 36, wherein said etching is performed in a reaction chamber.39. The process of claim 38, wherein said at least one fluorocarbon andsaid ammonia are flowed into said reaction chamber such the flow rateratio of said fluorocarbon to said ammonia is not less than about 2:1.40. The process of claim 39, wherein said flow rate ratio is within therange of about 2:1 to about 40:1.
 41. The process of claim 40, whereinsaid flow rate ratio is within the range of about 3:1 to about 10:1. 42.The process of claim 36, wherein said etching is performed withoutforming an etch stop.
 43. The process of claim 42, wherein said contactopening is formed between side wall spacers on a pair of adjacent gatestacks formed over said substrate.
 44. The process of claim 43, whereinsaid etching is performed at a temperature within the range of about −50to about 80 degrees Celsius.
 45. The process of claim 44, wherein saidetching is performed at a temperature within the range of about 0 toabout 80 degrees Celsius.
 46. The process of claim 45, wherein saidmethod further comprises removing said photoresist mask layer after saidetching.
 47. A method of preventing etch stop during a self-alignedcontact (SAC) etching of a semiconductor device which comprises addingammonia to at least one fluorocarbon used for said etching.
 48. Themethod of claim 47, wherein said ammonia is flowed to a reaction chambercontaining said device at a flow rate within the range of about 2 sccmto about 6 sccm.
 49. The method of claim 48, wherein said ammonia isflowed to said reaction chamber at a flow rate within the range of about2 sccm to about 5 sccm.
 50. The method of claim 49, wherein said ammoniais flowed to said reaction chamber at a flow rate not exceeding about 4sccm.
 51. The method of claim 50, wherein said at least one fluorocarbonis flowed into said reaction chamber with said ammonia.
 52. The methodof claim 51, wherein said fluorocarbon is flowed into said reactionchamber so as to have a flow rate which is not less than about 15 timesthe flow rate of said ammonia.
 53. The method of claim 52, wherein theflow rate ratio of said fluorocarbon to said ammonia is within the rangeof about 3:1 to about 40:1.
 54. The method of claim 53, wherein saidflow rate ratio is within the range of about 4:1 to about 20:1.
 55. Themethod of claim 52, wherein the flow rate ratio of said fluorocarbon tosaid ammonia is not greater than about 20:1.
 56. The method of claim 47,wherein said ammonia is added substantially simultaneously with saidfluorocarbon.
 57. The method of claim 47, wherein said ammonia is addedto a mixture comprising at least two fluorocarbons. 58.The method ofclaim 50, wherein said ammonia is added to a mixture comprising at leastthree fluorocarbons.
 59. A method of preserving a side wall spacersurrounding a gate stack during a self-aligned contact etch, whereinsaid gate stack is formed over a substrate in a semiconductor device,which comprises contacting said spacer with a combination of at leastone fluorocarbon and ammonia so as to form a protective layer over saidspacer.
 60. The method of claim 59, wherein said protective layer isformed to a thickness which is about 5 to 200 Angstroms in thickness.61. The method of claim 60, wherein said at least one fluorocarbon andsaid ammonia are flowed together over said side wall spacer such thatthe flow rate ratio of said fluorocarbon to said ammonia is not lessthan about 3:1.
 62. The method of claim 61, wherein said flow rate ratiois within the range of about 3:1 to about 20:1.
 63. The method of claim62, wherein said self-aligned contact etch provides an opening to saidsubstrate through an insulative layer formed over said substrate.
 64. Amethod of forming a conductive plug inside a contact opening in aninsulative layer between adjacent gate stacks formed over a substrate ina semiconductor device, comprising: contacting said insulative layerwith a plasma etchant mixture containing ammonia and at least onefluorocarbon at a temperature within the range of about −50 to about 80degrees Celsius so as to form a self-aligned contact opening in saidinsulative layer between said gate stacks without an etch stop, whereinsaid contacting further forms a protective layer over opposed side wallspacers which have been formed over said gate stacks; depositing aconductive plug inside said opening such that said conductive plug isseparated from said side wall spacers by said protective layer.
 65. Themethod of claim 64, wherein said contacting is performed by flowing saidammonia over said device in a reaction chamber at a flow rate within therange of about 2 sccm to about 6 sccm.
 66. The method of claim 64,wherein said fluorocarbon is at least one member selected from the groupconsisting of C₄F₈, C₄F₆, C₅F₈, CF₄, CHF₃, and CH₂F₂ and is flowed oversaid device at a flow rate within the range of about 10 sccm to about 45sccm.
 67. The method of claim 66, wherein said mixture comprises atleast two fluorocarbons and said flow rate ratio of each saidfluorocarbon to said ammonia is within the range of about 3:1 to about20:1.
 68. The method of claim 67, wherein said mixture comprises threefluorocarbons and said flow rate ratio is within the range of about 4:1to about 10:1.
 69. The method of claim 64, wherein said protective layeris a nitrogen containing layer.
 70. The method of claim 64, wherein saidtemperature is a pedestal temperature and said range is from about 0 toabout 50 degrees Celsius.